Method for assessing the result of a surface treatment performed on a workpiece by particle blasting

Abstract

Methods for assessing the result of a surface treatment carried out on a workpiece by particle blasting are disclosed. It is generally common to known automatic methods that they directly determine the covered portion of the surface. Proceeding from the usual definition of the usual 98% degree of coverage as “completely blasted” results in an error in the determination of the corresponding area of 1% to a distortion of the measurement result by 0.98%. In the disclosed method measuring points are identified as not hit by a particle of the particle beam when both a detected surface level is above a level located about a predetermined height threshold value lower than a target level, and a detected gradient falls below a predetermined gradient threshold value.

The invention claimed is: 
     
         1 . A method for assessing a result of a surface treatment carried out on a workpiece by means of particle blasting, wherein the method comprises:
 (1) recording of an optical measuring method a surface machined by means of particle blasting in a spatially resolved manner and, in each case for spatially resolved measuring points, determining:
 a. a surface level, and 
 b. a value of a local gradient with respect to adjacent measurement points; 
   (2) comparing the determined surface level with a target level expected for an untreated workpiece at a measuring location of a measurement point, and determining a deviation, and either:   (3a.1) identifying as measuring points not hit by a particle of the particle beam such measurement points for which:
 a. the determined surface level as per (1) a. is above a level located about a predetermined height threshold value lower than the target level, and 
 b. the doted determined gradient as per (1) b. falls below a predetermined gradient threshold value; 
   (3a.2) determining a portion of the surface that is not covered by the particle beam by dividing the number of measuring points identified as not hit by a particle of the particle beam as per (3a.1) by the total number of determined measuring points, and/or   (3b) determining a distribution of the deviation and a Weibull distribution parameter thereof, wherein an excessively low hit of the workpiece with the particle beam is assumed when the Weibull parameter is below a predetermined value;   wherein one of a white light interferometry, laser light section sensors, a stereo chamber system and/or a shape-by-shading method is used as the optical measurement method; and   wherein the spatially resolved recording of the surface machined by means of particle blasting is carried out with the aid of an optical measuring device.   
     
     
         2 . The method according to  claim 1 , wherein the spatially resolved recording of the surface machined by means of particle blasting is carried out with the aid of the optical measuring device arranged on a cobot. 
     
     
         3 . The method according to  claim 1 , wherein the values for the height threshold value and/or for the gradient threshold value are determined on the basis of an analysis of a reference pattern processed with a specific particle beam with predetermined particles and blast parameters and/or of a simulation model of a machining pattern produced for such a processing operation. 
     
     
         4 . The method according to  claim 1 , wherein the excessively low hit of the workpiece with the particle beam is assumed when the Weibull parameter is below a value in a range of 2.5 to 3.4. 
     
     
         5 . The method according to  claim 1 , wherein the excessively low hit of the workpiece with the particle beam is assumed when the Weibull parameter is below a value in a range of 2.9 to 3.1. 
     
     
         6 . The method according to  claim 1 , wherein the spatially resolved recording of the surface machined by means of particle blasting is carried out with the aid of the optical measuring device arranged on a stand. 
     
     
         7 . The method according to  claim 1 , wherein the spatially resolved recording of the surface machined by means of particle blasting is carried out with the aid of the optical measuring device arranged on a robot. 
     
     
         8 . The method according to  claim 1 , wherein the spatially resolved recording of the surface machined by means of particle blasting is carried out with the aid of optical measuring device having a laser targeting apparatus.